The days that smokers can light up cigarettes inside their apartments in unincorporated San Mateo County may be numbered.

On Tuesday, the Board of Supervisors is scheduled to consider approving an ordinance that would ban smoking inside apartments, condominiums and other multiple-housing units. Health officials contend cigarette smoke can creep through floors, walls and air systems, exposing other residents to its dangers.

Electronic cigarettes would be treated the same way, under the proposed ordinance. And like regular cigarettes, they also would be prohibited in public workplaces.

According to a memo by county supervisors Carole Groom and Adrienne Tissier, who are pushing the anti-smoking legislation, unnamed scientific studies show that electronic smoking devices emit nicotine in released vapor, as well as other harmful elements such as lead.

Medical marijuana would be exempted.

The law would apply to all housing facilities with two or more units and at least one shared ceiling, floor, wall or ventilation system. It also would pertain to any multi-unit residential building owned or leased by San Mateo County, no matter where, according to the memo.

But the ban would not affect hotels, motels, residential care and assisted living facilities.

The ordinance would take effect 30 days after its approval in common areas and newly rented or sold units. But it wouldn’t impact current residents until 14 months later.

The law allows landlords to establish designated smoking areas as long as they have clearly marked perimeters with conspicuous signs and are at least 30 feet from doors, windows and other openings to non-smoking spaces, according to the memo.

Smokers who violate the ordinance could be fined up to $100 for the first infraction, up to $200 for the second infraction and up to $500 for each additional offense within a year. After three violations, the next one would be charged as a misdemeanor. Each day a person violates the law would be considered a separate violation.

Primarily affected would be North Fair Oaks and unincorporated areas of Redwood City, where 105 of the 135 multi-unit facilities in the unincorporated county are located.

The North Fair Oaks Community Council, a county advisory group, endorsed the ordinance at its May 22 meeting.

The local division of the California Apartment Association helped shape the law, according to Groom and Tissier’s memo. A representative of the association could not be reached for comment Friday.

When the idea of a ban was discussed at a March meeting of the Board of Supervisors, a representative of the landlord group said local surveys show that tenants prefer housing with smoke-free areas, but the organization didn’t believe an outright ban was warranted.